在一个按钮上添加单击事件,程序倒是没有报错。可在模拟器里运行的时候,点击按钮就貌似出现BUG了。这是我的程序。package com.example.helloandroid;import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button aboutbutton = (Button)findViewById(R.id.about_button);
aboutbutton.setOnClickListener( new OnClickListener(){
public void onClick(View v){
switch(v.getId()){
case R.id.about_button:
Intent i = new Intent(new MainActivity(),AboutActivity.class);
startActivity(i);
break;
}
}
});
}}
这个是点击按钮后的log.
12-07 15:37:35.030: E/AndroidRuntime(880): FATAL EXCEPTION: main
12-07 15:37:35.030: E/AndroidRuntime(880): java.lang.NullPointerException
12-07 15:37:35.030: E/AndroidRuntime(880): at android.content.ContextWrapper.getPackageName(ContextWrapper.java:135)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.content.ComponentName.<init>(ComponentName.java:75)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.content.Intent.<init>(Intent.java:3491)
12-07 15:37:35.030: E/AndroidRuntime(880): at com.example.helloandroid.MainActivity$1.onClick(MainActivity.java:22)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.view.View.performClick(View.java:4202)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.view.View$PerformClick.run(View.java:17340)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.os.Handler.handleCallback(Handler.java:725)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.os.Handler.dispatchMessage(Handler.java:92)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.os.Looper.loop(Looper.java:137)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.app.ActivityThread.main(ActivityThread.java:5039)
12-07 15:37:35.030: E/AndroidRuntime(880): at java.lang.reflect.Method.invokeNative(Native Method)
12-07 15:37:35.030: E/AndroidRuntime(880): at java.lang.reflect.Method.invoke(Method.java:511)
12-07 15:37:35.030: E/AndroidRuntime(880): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-07 15:37:35.030: E/AndroidRuntime(880): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-07 15:37:35.030: E/AndroidRuntime(880): at dalvik.system.NativeStart.main(Native Method)
import android.app.Activity;
import android.content.Intent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button aboutbutton = (Button)findViewById(R.id.about_button);
aboutbutton.setOnClickListener( new OnClickListener(){
public void onClick(View v){
switch(v.getId()){
case R.id.about_button:
Intent i = new Intent(new MainActivity(),AboutActivity.class);
startActivity(i);
break;
}
}
});
}}
这个是点击按钮后的log.
12-07 15:37:35.030: E/AndroidRuntime(880): FATAL EXCEPTION: main
12-07 15:37:35.030: E/AndroidRuntime(880): java.lang.NullPointerException
12-07 15:37:35.030: E/AndroidRuntime(880): at android.content.ContextWrapper.getPackageName(ContextWrapper.java:135)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.content.ComponentName.<init>(ComponentName.java:75)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.content.Intent.<init>(Intent.java:3491)
12-07 15:37:35.030: E/AndroidRuntime(880): at com.example.helloandroid.MainActivity$1.onClick(MainActivity.java:22)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.view.View.performClick(View.java:4202)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.view.View$PerformClick.run(View.java:17340)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.os.Handler.handleCallback(Handler.java:725)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.os.Handler.dispatchMessage(Handler.java:92)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.os.Looper.loop(Looper.java:137)
12-07 15:37:35.030: E/AndroidRuntime(880): at android.app.ActivityThread.main(ActivityThread.java:5039)
12-07 15:37:35.030: E/AndroidRuntime(880): at java.lang.reflect.Method.invokeNative(Native Method)
12-07 15:37:35.030: E/AndroidRuntime(880): at java.lang.reflect.Method.invoke(Method.java:511)
12-07 15:37:35.030: E/AndroidRuntime(880): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
12-07 15:37:35.030: E/AndroidRuntime(880): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
12-07 15:37:35.030: E/AndroidRuntime(880): at dalvik.system.NativeStart.main(Native Method)
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修改为Intent i = new Intent(MainActivity.this,AboutActivity.class);
然后确保你的AboutActivity在Manifest.xml中有注册
这样就可以启动另一个Activity了。
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.helloandroid"
android:versionCode="1"
android:versionName="1.0" > <uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="17" /> <application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/activity_main_title"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.helloandroid.MainActivity"
android:label="@string/continue_lable" >
<intent-filter>
<action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.helloandroid.AboutActivity"
android:label="@string/about_title" >
</activity>
</application></manifest>
Intent i = new Intent(new MainActivity(),AboutActivity.class);
startActivity(i);
You cannot write : new XXXActivity().new MainActivity() 改为 MainActivity.this即可。